2007 Sensory Physiology

Efferent function in the cochlea

  • hair cells are innervated by both afferent and efferent fibres
    • afferent fibres to the outer hair cells are not shown in this figure
  • efferent fibres innervating the organ of Corti have their cell bodies in the brainstem, and are part of a reflex circuit via collateral connections arising from the cochlear nucleus
  • medial efferents form large synapses with the cell bodies of the outer hair cells
    • lateral efferents innervate the afferent terminals underlying the inner hair cells
Efferent innervation
Effects of OHC stimulation on BM motion
  • descending control of the OHCs allows for reflex control of basilar membrane motion
  • activation of efferent fibres via stimulation of the contralateral ear (filled circles) causes an increase in acoustic thresholds
    • i.e., the presence of sound in one ear means that it takes a louder than normal sound in the opposite ear in order to produce the same amplitude of basilar membrane motion --- the normal graph (open circles) shifts to the right
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